Electric furnace dome

ABSTRACT

Electric furnace dome that is made especially of ceramic material and which has the necessary openings for at least electrodes and material feed, at which time the dome&#39;s center (2) inside of the tube systems (3) is cooled at least around the openings with the aid of spiral tube systems (5,7,8,9) whose tube systems (3,5,7,8,9) form a part of the dome&#39;s support system.

This invention relates to an electric furnace dome that is hermetic andmade of ceramic material and that is cooled at its center and supportedwith the aid of external tube systems to improve durability.

The simplest and most inexpensive dome construction is one that is madeof bricks or cast from mass, the dome being in reality dome-shaped, inother words the surface is outwards in the shape of a round ball. If thedome is built of ceramic mass, its structure is generally quite weak,which is the reason why it must be supported at those points where thereare for example openings. Not even supporting however always helps, butthe resulting construction is still weak at least under situations ofmalfunction. Fully supported brick domes that have a planar surface areaalso used. Such structures are generally very expensive and difficult torepair and service. Externally cooled domes have become known as a thirdalternative, as for example the box beam construction that has becomeknown from the Finnish patent application No. 783705. A drawback of thisdome also is its expensiveness, as well as the energy losses caused bygreat amounts of cooling water and the danger of explosion in the caseof leakage, electrode breakage or other such inconvenience toproduction.

The purpose of this invention is to avoid the drawbacks of domes inaccordance with technical level and achieve an electric furnace domewhose construction expenses as well as costs of using are moderate andwhich is hermetic and endures use.

The characteristical features of the invention are given in theaccompanying patent claims.

The invention is described in more detail in the following by referringto the accompanying drawings of which

FIG. 1 illustrates the side view along the cutline in

FIG. 2 of an electric furnace dome in accordance with the invention,

FIG. 2 illustrates an electric furnace dome in accordance with theinvention viewed from above.

An electric furnace dome in accordance with the invention is made ofceramic material (mass and/or brick) and is constructed so that thedome's stationary edge 1 is separated from the easily repairable orchangeable center 2 by water-cooled tube systems 3 that are supportedfrom outside of the dome. Further the dome's center 2 which is undergreat strain is watercooled by spiral tube systems that are inside ofthe dome structure. In the figures the spiral tube systems in the centerof the dome that are around the openings 4 for the electrodes areindicated by the number 5, the spiral tube systems around the materialfeed openings 6, some of which are in the center of the dome and thuswatercooled and some on the edge of the dome, are indicated by thenumber 7, and the spiral tube systems that are directly in the center ofthe dome are indicated by the numbers 8 and 9. The spiral tube systemsare at the same time a part of the dome's watercooled support system,because the spiral tube systems are supported at both of their ends bysupporting rods 10 from outside of the dome, as FIG. 1 illustrates forexample for the spiral tube system 9.

The input pipes 11 that are fastened to the openings 6 for raw materialfeed are equipped with ceramic lining and are tightened to thecorresponding part 2 and 1 on the dome with a thin insulating layer 12that consists of ceramic wool and/or fibre and that due to watercoolingendures the electric furnace's temperatures well. The effect of thewatercooling reaches however beyond the insulating layer which to acertain extent increases the dome's tenacity to endure practicalcircumstances in the possible cases of malfunction caused by for examplethe overheating of the furnace.

Further the raw material's input pipes 11 go through the dome and thatsection 13 that is on the inside of the furnace is a fixed part of thedome's cooling system and thus increases the dome's hermetic sealingbecause the input pipes are watercooled at that part of the dome and onthe inside of the furnace by a spiral tube system 7 that is supportedfrom outside of the dome.

The openings 4 for electrodes in an electric furnace dome in accordancewith the invention are watercooled and hermetically sealed in twostages. Water spiral tube system 5 that is supported from outside of thedome is mounted in the dome center's 2 refractory masonry, the waterspiral tube system being thus at the same time a part of the dome'swatercooled support system around the electrode opening. Spiral tubesystem advantageously improves the durability of the area around theelectrode opening which to a certain extent increases the dome'shermetic sealing. Further a water seal's casing 15 which is made ofrefractory steel plate and is equipped with external support rods 14 isabove the hole for the electrode, the water in the seal being separateor a part of the water circulating through the spiral tube systems. Thewater seal aids in the dome's hermetic sealing especially between thecurrent contact pack and the dome's center 2.

In the figures the number 16 indicates an opening through which vapoursand gases are removed from the furnace. Number 17 on the other handindicates a watercooled sand seal which aids in achieving sealingbetween the dome's edge 1 and the pot 18 and number 19 indicates thepot's external watercooling system where the cooling water in the spiraltube systems is led, as is shown by the arrow in FIG. 1.

The heat loss of an electric furnace dome in accordance with theinvention is moderate because of the selection of favourable material.For processtechnical reasons ceramic mass or refractory bricks may beused as the construction material for the whole dome. The dome may alsobe constructed so that the edge 1 and the center 2 of the dome are madeof different materials, from mass or bricks. However in allapplications, tube systems 3 are used to separate the dome's edge 1 fromthe center 2, at which time the dome's edge 1 is stationary and ifnecessary the center 2 may be advantageously repaired or changed inpossible cases of malfunction.

The acquisition price of the dome construction that is the object of theinvention is also moderate on account of inexpensive constructionmaterials. As a result of external supports it also lasts sufficientlylong enough and requires little service and repair. Further the tubesystems 3 separating the dome's edge 1 and the center 2 make theplacement and operating of devices connected to the dome easier as wellas servicing and repairing the dome.

In other words the principle of the dome construction in accordance withthe invention is to make as good and profitable use as possible of allof the tenacity, insulatory, refractory, and other such characteristicsof the refractory material as well as the advantages of external supportand watercooling.

This is achieved by choosing the refractory ceramic material and masonryconstruction so that the dome is in principle under normal conditionsself-supporting and extra strains as well as deficiencies in materialand construction are taken care of by external support as well as bywatercooling at the most critical points, such as the electrodes andinput pipes and at the center of the furnace. The purpose of thewatercooling is to protect the support systems that are constructed inthe form of tube spirals and are at the critical points of the dome andof the openings as well as to maintain the temperature of the ceramicmaterial at moderate temperatures as far as operating conditions areconcerned without however unnecessarily cooling the molten charge.

What is claimed is:
 1. In an electric furnace dome having top and bottomsurfaces, and having at least one opening for an electrode, theimprovement comprising(a) a water-carrying spiral tube system embeddedbetween said surfaces for water-cooling the dome and centered aroundsaid electrode opening, and (b) means for supplying cooling water tosaid spiral tube system and for supporting the dome, said meansincluding a portion of said spiral tube system that extends upwardly andaway from said top surface of the dome.
 2. In an electric furnace domehaving top and bottom surfaces and respective openings at least for oneelectrode, for the insertion of raw material, and for the exhaust ofgases, and having a central portion and an outer portion, said electrodeopening being in said central portion, the improvement comprising(a)water-carrying spiral tube systems embedded between said surfaces forwater-cooling the dome, located only in said central portion, and atleast one spiral tube system being centered around each opening in saidcentral portion; and (b) means for supplying cooling water to saidspiral tube systems and for supporting the dome, said means including aportion of each of said spiral tube systems that extends upwardly andaway from said top surface of the dome.
 3. An electric furnace dome asin claim 2, wherein said dome is made of ceramic material.
 4. Anelectric furnace dome as in claim 2, further comprising a secondwater-carrying tube system embedded between said surfaces andsurrounding said central portion of the dome, for further water-coolingthe dome.
 5. An electric furnace dome as in claim 4, wherein said domeand said second water-carrying tube system are substantially circular.6. An electric furnace dome as in claim 2, further comprising at leastone water seal mounted on said central portion of said dome for sealingand water-cooling said electrode opening, and wherein said means forsupplying cooling water are connected to said water seal so as tocirculate the same water sequentially through said seal and at least oneof said tube systems.